Field of the Invention
This invention relates to earthboring, in general, and directional well drilling in particular.
Description of Related Art
There are several known processes for steering the axial direction of a wellbore. The older, original, processes utilize devices such as “whipstocks” to deflect a drill string from vertical as it is rotated by surface positioned drive power. More recently, in the past 30 to 40 years, downhole drilling motors have been developed to limit rotary bit drive motion to approximately 10 feet of the bottom distal end of the drill string. Such downhole drilling motors are powered by fluid delivered along the drill string bore from surface positioned pumps. The upper length of the drill string remains rotatively static.
Among the several advantages of downhole motor drilling is the opportunity to deviate the boring direction of the drill bit along a controlled path. As a consequence, fluid mineral producers are no longer limited to the “production face” of a well corresponding to the thickness of the mineral bearing strata. With the advantage of direction controlled drilling, producers may advance the production face of a well thousands of feet along the planar lay of the strata. Hence, a greater percentage of the in situ mineral present in the strata may be produced.
In drilling processes using a downhole motor, drilling fluid is circulated under pressure through the drill string and back to the surface along the borehole annulus as in conventional drilling methods. However, the pressurized drilling fluid is directed through the power section of the downhole motor to generate power to rotate the drill bit.
In directional drilling, the path of the drill bit is deviated in a desired direction by means of a bent housing or a bent sub, typically disposed between the power section and the bearing assembly of a downhole motor. Although bent subs and bent housings may be fashioned with a fixed bend angle, it is commonly advantageous for a bent housing or bent sub to comprise an assembly of components whereby the bend angle is adjustable between being zero and some maximum bend angle.
Examples of known types of adjustable bent housings and bent subs may be seen in U.S. Pat. No. 4,077,657 to K. H. Trzeciak, U.S. Pat. No. 4,813,497 to K. H. Wenzel, U.S. Pat. No. 5,125,463 to R. S. S. Livingstone et al, U.S. Pat. No. 5,168,943 to T. E. Falgout, Sr., U.S. Pat. No. 5,343,966 to K. H. Wenzel et al and U.S. Pat. No. 6,550,818 to L. E. Robin